Abnormal Plumage Survey

Hundreds of birds with unusual marking have been reported in the BTO abnormal plumage survey.

Leucistic Blackbird, Oxfordshire. Pic BTO / Dennis Simpkin

Across the country, householders have been seeing Blackbirds with strange white markings.

The condition, typically referred to as ‘leucism’, is one of a number of plumage abnormalities to have been reported through the BTO abnormal plumage survey, preliminary results from which have just been published.

Survey results

In less than a month, the survey has clocked up nearly 700 sightings, encompassing more than 35 different species.

Three quarters of records have been of leucistic birds and, of these, nearly half have been Blackbirds.

Leucistic birds may be confused with albino individuals, but the latter have pink, instead of dark eyes, and only account for 12% of survey records to date.

It is not yet clear why Blackbirds appear to be particularly affected.

It could be that they are unusually susceptible to the condition. However, being black or, in the case of female Blackbirds dark brown, any light-coloured feathers show up particularly clearly. Indeed, several other species with all-black, or mostly black, plumage have been spotted with white feathers fairly often, including Carrion Crow (49 records) and Jackdaw (40).

Strange sightings

Many other strange-looking birds have also been seen.

Of the 28 ‘melanistic’ individuals recorded, which have an excess of dark-coloured feather pigmentation patterns, almost half have been Great Tits or Blue Tits, with their normally white cheeks and yellow bellies becoming dark-coloured.

Other fascinating abnormalities have included a family of four chocolate-brown Jackdaws in County Antrim, a Greenfinch with orange feathers in the West Midlands and a Goldfinch with an orange rather than a red face in East Sussex.

Perhaps the most striking photo sent into the survey to date has been an all-white Starling, seen in Prestatyn, North Wales.

Dr Tim Harrison, of the BTO garden ecology team, said: “The diversity of species recorded through the survey is impressive, ranging from common garden birds, such as House Sparrow and Chaffinch, to less frequent visitors, such as an all-white Buzzard in Aberdeenshire and a leucistic Coot in Norfolk.

“On a handful of occasions, birds have looked so unusual that participants have simply had to write ‘species unknown’.”

“The most northerly survey record to date has been from Shetland, from where we received a report of a Blackbird with white feathers around its eyes, making it look as though it is wearing spectacles.

“The most southerly record has been a leucistic House Sparrow seen last year on St Mary’s, Isles of Scilly.”

The BTO survey

The BTO Abnormal Plumage Survey is a project to find out about birds with unusual plumage characteristics in gardens.

The survey was launched by the Garden Ecology Team in December 2011 and is centred on pigmentation irregularities.

Anecdotal reports show that birds can turn up in gardens with a variety of unusually-coloured feathers, but questions about which species are affected most frequently, in what ways and where these birds are found remain unsolved.

The Abnormal Plumage Survey is gathering data to explore these questions.

If you have ever seen a bird with unusual plumage in your garden, they would really like to hear from you.

Please note that plumage abnormalities associated with feather loss are not being recorded through the survey.